Mary Ann Sullivan married Henry Sherman Niles in 1858. Mary and "Sherman" had several children: Cora Virginia, Eliza Ann, Sarah Lilly, Henry Lansing, Mary Edith, Anna Jane, and Harriet Cynthia Niles. In 1860 the family was living at Liberty Township, Scott County, Iowa. In 1870 they lived at Windsor Township, Dane County, Wisconsin. She was widowed in 1875 at the age of 37, when her youngest child was just 5 months old. In 1880 the family was still living at Windsor Township, Dane County Wisconsin. By 1892 Mary and her family were living with her sister, Sarah Ann Sullivan Niles, at Fort Totten, Benson County, North Dakota. Mary's sister, Sarah, had married Stephen Lansing Niles (brother of Henry Sherman Niles).